Mammalian cells are a widely used in vitro model in diagnostic and medical applications. For example, mammalian cells may be used for screening drugs, studying molecular pathways, or for the production of therapeutics drugs. Mammalian cells can also be used for cell therapy.
Mammalian stem cells are primal cells found in all mammalian organisms that retain the ability to renew themselves through mitotic cell division and can differentiate into a diverse range of specialized cell types. Embryonic stem cells (ES cells) are cultures of cells derived from the epiblast tissue of the inner cell mass of a blastocyst.
Due to their two fundamental attributes of unlimited expansion and pluripotency, stem cells, and in particular human embryonic stem (hES) cells have gained considerable interest for use in cell replacement therapy as well as in drug discovery.
However, the use of embryos for obtaining of ES cells is controversial and raises ethical issues. Alternative sources of pluripotent cells have therefore been investigated.
Induced pluripotent stem cells (iPS cells) are a type of pluripotent stem cells artificially derived from a non-pluripotent, typically an adult somatic cell, by inducing a “forced” expression of certain genes.
iPS cells were first produced in 2006 from mouse cells (Takahashi et al Cell 2006 126:663-76) and in 2007 from human cells (Takahashi et al. Cell 2007 131-861-72, Yu et al. Science 2007 318:1917). These authors demonstrated that it was possible to de-differentiate somatic cells by introducing reprogramming transcription factors into said somatic cells using a viral expression system.
However, the use of viral transduction poses several problems that hinder the development of such methods for use in therapy. Indeed, there exists a risk of genomic alteration of the target cell, and of oncogene expression.
Other authors have suggested the use of non-integrating episomal vectors for producing virus-free iPS cells (Yu et al. Science 2009, vol 324, p 797-801). However, the reprogramming efficiency remains low. Further, karyotype anomalies in one of the resulting iPS clones were later observed by these authors.
Recently, Zhou et al. have reported a non-genetic method for obtaining iPS cells (Zhou et al. Cell Stem Cell 2009, vol 4, p 381-384). These authors used poly-arginine recombinant proteins in order to introduce reprogramming factors into a target cell. However, this method is time-consuming and poorly amenable to large scale production, since each recombinant protein must be expressed and purified before introduction into the target cell.
Thus, there is still a need in the art for a fast, safe and efficient method for reprogramming a target cell, for example for obtaining induced pluripotent stem cells.